To home networks of recent years, a home-electric-appliance cooperation function has been introduced with which various home electric appliances are connected to a network by a home energy management system (HEMS) having a function of managing power usage for addressing an environmental issue, turning power ON and OFF from outside a house, and the like, in addition to cooperation of AV home electric appliances by internet protocol (IP) connection using an Ethernet (registered trademark) or a wireless local area network (LAN). However, computational performance of some home electric appliances is not sufficient to provide a communication function, and it is hard to provide some home electric appliances with a communication function in terms of cost.
In order to solve such a problem, Patent Literature 1 discloses a technique of efficiently establishing inter-device communication between limited transmission devices by performing communication using plural monochromatic light sources of illumination light among optical spatial transmission devices which transmit information to free space.